Google released a new monthly batch of security patches for Android, fixing a dozen critical vulnerabilities that could allow attackers to compromise devices. One of the mitigated issues is a bit-flipping attack against memory chips that could lead to privilege escalation, but a more widespread rooting vulnerability in the Linux kernel remains unpatched.

While Google releases firmware updates for its Nexus and Pixel devices on the first Monday of every month, the security patches are shared with third-party device manufacturers one month in advance and are also contributed later to the Android Open Source Project to benefit the entire ecosystem.

Like it has done in recent months, Google has split this month’s security fixes into several “security patch levels,” to make it easier for manufacturers to deploy only fixes that apply to specific devices. The security patch level is a date string displayed in Android’s settings under “About phone” and indicates that the firmware contains all Android security patches up to that date.

The new 2016-11-01 patch level contains fixes for flaws in Android’s own components. It addresses two critical vulnerabilities, 16 high-risk flaws and 10 medium-risk ones.

One of the critical flaws is located in the Mediaserver component, which has been a major source of serious Android vulnerabilities over the past year. The flaw can be exploited by tricking users into downloading or opening a specially crafted media file.

The second critical flaw is located in the libzipfile library and could enable malicious applications to execute code within the context of a privileged process. This can lead to a full device compromise that requires reflashing the operating system to fix.

The second patch level is 2016-11-05 and primarily includes fixes for vulnerabilities in kernel drivers for various hardware components. This level covers 21 critical vulnerabilities, 23 high-risk ones and 10 with a moderate impact.

The critical flaws are located in the kernel file system, SCSI driver, media driver, USB driver, ION subsystem, networking subsystem and sound subsystem, as well as in the Nvidia GPU driver and Qualcomm’s crypto driver, bootloader and other components.

One of the patches for the ION memory allocator is intended to mitigate a physical attack against DRAM (dynamic random-access memory) chips that could be exploited by applications to gain root access on a device. The attack is known as Drammer and was devised by researchers from the Vrije Universiteit Amsterdam in the Netherlands, the Graz University of Technology in Austria, and the University of California in Santa Barbara.

The third patch level is 2016-11-06 and covers a privilege escalation vulnerability in the memory subsystem of the Linux kernel that was disclosed a few weeks ago. The flaw, which the security community dubbed Dirty COW (copy-on-write) has existed in the Linux kernel for the past nine years and is already being exploited in the wild.

Google has not patched this vulnerability in its Nexus and Pixel devices yet and will probably do it next month. However, device manufacturers can address the flaw by importing the upstream fix that was included in the Linux kernels versions 3.10 and 3.18. The flaw was disclosed after this month’s patch levels had already been defined, which is why Google refers to the 2016-11-06 patch level as “supplemental.”